Process for the production of diaryl carbonates

ABSTRACT

A process for catalytic production of diaryl carbonates by oxidative carbonylation of aromatic hydroxy compounds with carbon monoxide and oxygen achieves water removal during reaction by a process comprising the steps of: removing a liquid stream from an oxidative carbonylation reaction mixture in a reaction vessel, subjecting the liquid stream to reduced pressure, and returning at least a portion of dried liquid stream to the reaction vessel. Typical catalyst systems for oxidative carbonylation contain (A) at least one Group  8, 9 , or  10  metal having an atomic number of at least  44  or a compound thereof; (B) at least one alkali metal salt; (C) at least one metal co-catalyst; (D) at least one activating organic solvent; and (E) optionally, at least one base.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of copending U.S.application Ser. No. 09/736,885, filed Dec. 14, 2000, which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention is related to an improved process for theremoval of undesirable water from a chemical reaction for producingproducts in which water is deleterious to the process and/or productsproduced therefrom. In particular, the products are carbonate esters,and more particularly diarylcarbonates, prepared by the oxidativecarbonylation of aromatic hydroxy compounds, such as by the reactionwith carbon monoxide and oxygen in the presence of a catalyst generallycontaining a metal of group 8, 9, or 10 of the Periodic Table ofElements and a co-catalyst. The process of this invention allowscontinuous removal of water without depressurization of a reactionvessel.

[0003] Water removal in the oxidative carbonylation of aromatic hydroxycompounds to make diarylcarbonates is a desirable process since itenhances the productivity of the reaction and thus reduces reactor costper unit mass of product. This is demonstrated by the improvementobtained when molecular sieves are used for water removal in reactionsto make diphenyl carbonate (DPC), as described in U.S. Pat. No.5,399,734 and in co-pending application Ser. No. 09/224,162, filed Dec.31, 1999.

[0004] U.S. Pat. No. 5,625,091 describes water removal from oxidativecarbonylation reaction mixtures under reduced pressure. U.S. Pat. No.5,498,472 describes water removal from oxidative carbonylation reactionmixtures by excess process gas flow at relatively low pressures. Both ofthese latter two methods are specific to reaction mixtures containing aspecified catalyst type which employs a quaternary salt and a base. Aninert stripping agent has also been used for removing water fromreaction mixtures for oxidative carbonylation of aromatic hydroxycompounds as described in U.S. Pat. No. 5,917,078.

[0005] The problem to be solved is to develop a reaction process whichremoves water from an oxidative carbonylation reaction mixturecontinuously without the requirement of using an entrained gas processor water absorbing agent. In this manner the water content inside thereactor or reactors may be kept below a prescribed value, in a mannerwhich retains the activity of the catalyst system and minimizes theutilities requirements.

BRIEF SUMMARY OF THE INVENTION

[0006] After careful study the present inventors have discovered methodsfor removing water of reaction in an integrated process for oxidativecarbonylation of aromatic hydroxy compounds which avoids the problems ofearlier methods. Thus, in one of its embodiments the present inventionis a method for preparing a diaryl carbonate which comprises contactingat least one aromatic hydroxy compound with oxygen and carbon monoxidein the presence of an amount effective for carbonylation of a catalystcomposition comprising the following and any reaction products thereof:

[0007] (A) at least one Group 8, 9, or 10 metal having an atomic numberof at least 44 or a compound thereof;

[0008] (B) at least one alkali metal salt;

[0009] (C) at least one metal co-catalyst;

[0010] (D) at least one activating organic solvent; and

[0011] (E) optionally, at least one base,

[0012] wherein reaction water is removed by a process comprising thesteps of:

[0013] (i) removing a liquid stream from an oxidative carbonylationreaction mixture;

[0014] (ii) transferring the liquid stream to a flash vessel wherein theliquid stream to subjected to reduced pressure, whereby a majority ofthe water is removed;

[0015] (iii) returning at least a portion of a dried liquid stream to areaction vessel; and

[0016] (iv) optionally adding at least one of make-up aromatic hydroxycompound or other volatile constituent or catalyst component to thereaction vessel or to the dried liquid stream before return to thereaction vessel,

[0017] wherein at least a portion of diaryl carbonate is recovered froma liquid stream either before or after water removal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a flow diagram for a process which removes water.

[0019]FIG. 2 is another flow diagram for a process which removes water.

[0020]FIG. 3 is yet another flow diagram for a process which removeswater.

[0021]FIG. 4 is a graph of palladium turn-over number (TON) versus timefor a reaction mixture which was depressurized compared to a reactionmixture which was not depressurized using a catalyst system comprisingpalladium-copper-titanium.

[0022]FIG. 5 is a graph of palladium turn-over number (TON) versus timefor a reaction mixture which was depressurized compared to a reactionmixture which was not depressurized using a catalyst system comprisingpalladium-lead.

DETAILED DESCRIPTION OF THE INVENTION

[0023] For the sake of brevity, the constituents of the catalyst systemare defined as “components” irrespective of whether a reaction betweensaid constituents occurs before or during the carbonylation reaction.Thus, the catalyst system may include said components and any reactionproducts thereof. The terms “reactor” and reaction vessel” are usedinterchangeably.

[0024] Unless otherwise noted, the term “effective amount”, as usedherein, includes that amount of a substance capable of either increasing(directly or indirectly) the yield of the carbonylation product orincreasing selectivity toward an aromatic carbonate. Optimum amounts ofa given reactant can vary based on reaction conditions and the identityof other constituents, yet can be readily determined in light of thediscrete circumstances of a given application.

[0025] Any aromatic hydroxy compound convertible to a carbonate estermay be employed in the present invention. Suitable aromatic hydroxycompounds include monocyclic, polycyclic or fused polycyclic aromaticmonohydroxy or polyhydroxy compounds having from 6 to 30, and preferablyfrom 6 to 15 carbon atoms. Illustrative examples include mono- andpoly-hydroxy compounds such as phenol, alkylphenols, o-, m- or p-cresol,o-, m- or p-chlorophenol, o-, m- or p-ethylphenol, o-, m- orp-propylphenol, o-, m- or p-methoxyphenol, methyl salicylate,2,6-dimethylphenol, 2,4-dimethylphenol, 3,4-dimethylphenol, 1-naphtholand 2-naphthol, xylenol, resorcinol, hydroquinone, catechol, cumenol,the various isomers of dihydroxynaphthalene,bis(4-hydroxyphenyl)propane-2,2,α,α′-bis(4-hydroxyphenyl)p-diisopropylbenzene,and bisphenol A. Aromatic mono-hydroxy compounds are particularlypreferred with phenol being the most preferred. In the case ofsubstituents on the aromatic hydroxy compound, the substituents aregenerally 1 or 2 substituents and are preferably from C-1 to C-4 alkyl,C-1 to C-4 alkoxy, fluorine, chlorine or bromine.

[0026] When an aromatic hydroxy compound as a raw material is used as areaction solvent, then another solvent need not be used. However, thereaction mixture may also optionally contain at least one inert solvent,that is a solvent whose presence does not improve the yield of orselectivity toward the aromatic carbonate. Illustrative inert solventsinclude, but are not limited to, hexane, heptane, cyclohexane, methylenechloride, or chloroform.

[0027] Other reagents in the method of this invention are oxygen andcarbon monoxide, which react with the aromatic hydroxy compound to formthe desired diaryl carbonate. The carbon monoxide may be high-puritycarbon monoxide or carbon monoxide diluted with another gas which has nonegative effects on the reaction, such as nitrogen, noble gases, argon,or carbon dioxide. The oxygen used in the present invention may be highpurity oxygen, air, or oxygen diluted with any other gas which has nonegative effects on the reaction, such as nitrogen, noble gases, argon,or carbon dioxide. The concentration of inert gas in the reaction gasmay amount to 0 to about 60 volume %, preferably 0 to about 20, and morepreferably 0 to about 5 volume %. In a particular embodiment theconcentration of inert gas is 0 volume % and the reaction gas is free ofinert gas.

[0028] The composition of the reaction gases carbon monoxide and oxygencan be varied in broad concentration ranges. Preferably a carbonmonoxide: oxygen molar ratio (normalized on carbon monoxide) of1:(0.001-1.0) is employed, more preferably 1:(0.01-0.5) and still morepreferably 1:(0.02-0.3). The reaction gases are not subject to specialpurity requirements but care must be taken to ensure that no catalystpoisons such as sulfur or compounds thereof are introduced. In thepreferred embodiment of the process according to the invention, purecarbon monoxide and pure oxygen are used. In a further preferredembodiment of the process according to the invention, carbon monoxideand oxygen may be added independently of each other. The oxygenaddition, in this case, can take place, if desired, together with inertgas. When a reactor cascade is used instead of an individual reactor,the separate oxygen addition preferably proceeds in such a way that theoptimal oxygen concentration is ensured in each of the reactors.

[0029] The reaction gas, comprising carbon monoxide, oxygen and,optionally, an inert gas, may be typically introduced at a rate of about1 to about 100,000 liters (S.T.P.) per liter of reaction solution,preferably about 5 to about 50,000 liters (S.T.P.) per liter of reactionsolution and particularly preferably about 10 to about 10,000 liters(S.T.P.) per liter of reaction solution.

[0030] The catalyst employed herein contains at least one Group 8, 9, or10 metal having an atomic number of at least 44 or a compound thereof,preferably palladium. The palladium material useful as a catalyst(sometimes referred to hereinafter as palladium source) can be inelemental form or it can be employed as a palladium compound. Thepalladium material can be employed in a form that is substantiallysoluble in the reaction media or in a form which is substantiallyinsoluble in the reaction media, such as a supported- or polymer-boundpalladium species. Thus, useful palladium materials include elementalpalladium-containing entities such as palladium black, palladiumdeposited on carbon, palladium deposited on alumina and palladiumdeposited on silica; palladium compounds such as palladium chloride,palladium bromide, palladium iodide, palladium sulfate, palladiumnitrate, palladium carboxylates, palladium acetate and palladium2,4-pentanedionate; and palladium-containing complexes involving suchcompounds as carbon monoxide, amines, nitrites, phosphines and olefins.As used herein, the term “complexes” includes coordination or complexcompounds containing a central ion or atom. The complexes may benonionic, cationic, or anionic, depending on the charges carried by thecentral atom and the coordinated groups. Other common names for thesecomplexes include complex ions (if electrically charged), Wernercomplexes, and coordination complexes. Preferred in many instances arepalladium (I1) salts of organic acids, most often C₂₋₆ aliphaticcarboxylic acids, and palladium (II) salts of β-diketones. Palladium(II) acetate and palladium (II) 2,4-pentanedionate (also know aspalladium (II) acetylacetonate) are generally most preferred. Mixturesof palladium materials are also contemplated.

[0031] The quantity of the at least one Group 8, 9, or 10 metal catalystis not particularly limited in the process of the present invention. Aneffective amount of the at least one Group 8, 9, or 10 metal catalyst,particularly palladium, is, for example, an amount sufficient to provideabout 1 gram-atom of metal per 800-1,000,000, more preferably per4000-1,000,000, still more preferably per 40,000-200,000, and morepreferably per 65,000-100,000 moles of aromatic hydroxy compound fed tothe reactor. Aromatic hydroxy compound fed to the reactor includes thataromatic hydroxy compound fed directly to the reactor and that aromatichydroxy compound recycled to a reactor or added as make-up aromatichydroxy compound, all of which may include catalyst.

[0032] The catalyst employed herein also contains at least one salt withanion selected from tetrafluoroborates, hexafluorophosphates andhalides. In preferred embodiments the salt is an alkali metal salt,preferably an alkali metal halide, and more preferably a bromide such aslithium bromide, sodium bromide, or potassium bromide. Sodium bromide isoften most preferred by reason of its particular suitability andrelatively low cost.

[0033] Mixtures of the aforementioned salts are also suitable for use inthe invention. The at least one salt is typically present in thereaction mixture in an amount of about 1-2000 moles, preferably about2-1500 moles, and more preferably about 5-1000 moles per gram-atom ofGroup 8, 9, or 10 metal catalyst.

[0034] There also can be used in combination with the Group 8, 9, or 10metal catalyst and catalyst system at least one quinone and aromaticdiol formed by the reduction of said quinone or a mixture thereof.1,4-benzoquinone and hydroquinone are preferred. In addition, compoundssuch as 1,2-quinone and catechol, anthraquinone,9,10-dihydroxyanthracene, and phenanthrenequinone also can be used. Whenpresent, the at least one quinone and aromatic diol formed by thereduction of said quinone or a mixture thereof may be present in anamount of about 10-60, and preferably about 25-40 moles of quinoneand/or reduction product thereof per gram-atom of Group 8, 9, or 10metal catalyst.

[0035] In addition to the at least one Group 8, 9, or 10 metal catalysthaving an atomic number of at least 44 there is present in the reactionmixtures of the invention an effective amount of at least one metalco-catalyst (component C) containing a metal different from the at leastone Group 8, 9, or 10 metal. Suitable metal cocatalysts include allthose known in the art which promote formation of carbonate ester fromaromatic hydroxy compound under reactive conditions in the presence ofthe at least one Group 8, 9, or 10 metal catalyst having an atomicnumber of at least 44. Metal co-catalysts include elemental metals,metal compounds, and precursors thereof which may form catalyticallyactive metal species under the reaction conditions, it being possiblefor use to be made of the metal in various degrees of oxidation. Metalco-catalysts may be initially soluble in the reaction mixture orinitially insoluble as in supported- or polymer-bound metal co-catalystspecies. Alternatively, metal co-catalysts may be initially insoluble inthe reaction mixture and form soluble metal co-catalyst species duringthe course of the reaction. Illustrative metal co-catalysts includelead, copper, titanium, and cerium, either alone or in combination.Preferred metal co-catalysts comprise compounds of lead, particularlywhen used alone or in combination with at least one of titanium, copper,or cerium.

[0036] The at least one metal co-catalyst can be introduced to thecarbonylation reaction in various forms, including salts and complexes,such as tetradentate, pentadentate, hexadentate, or octadentatecomplexes. Illustrative forms may include oxides, halides, carboxylates(for example of carboxylic acids containing from 2-6 carbon atoms),diketones (including beta-diketones), nitrates, complexes containingcarbon monoxide, olefins, amines, phosphines and halides, and the like.Suitable beta-diketones include those known in the art as ligands forthe metal cocatalysts of the present invention. Examples include, butare not limited to, acetylacetone, benzoylacetone, dibenzoylmethane,diisobutyrylmethane, 2,2 -dimethylheptane-3,5-dione,2,2,6-trimethylheptane-3,5-dione, dipivaloylmethane, andtetramethylheptanedione. The quantity of ligand is preferably not suchthat it interferes with the carbonylation reaction itself, with theisolation or purification of the product mixture, or with the recoveryand reuse of catalyst components (such as palladium). A metalco-catalyst may be used in its elemental form if sufficient reactivesurface area can be provided.

[0037] The at least one metal co-catalyst is included in thecarbonylation catalyst system in effective amounts. In this context an“effective amount” is an amount of metal co-catalyst (or combination ofmetal co-catalysts) that increases the number of moles of aromaticcarbonate produced per mole of Group 8, 9, or 10 metal catalystutilized; increases the number of moles of aromatic carbonate producedper mole of salt utilized; or increases selectivity toward aromaticcarbonate production beyond that obtained in the absence of the metalco-catalyst (or combination of metal co-catalysts). Optimum amounts ofan metal co-catalyst in a given application will depend on variousfactors, such as the identity of reactants and reaction conditions.

[0038] One preferred class of metal co-catalysts comprises at least onelead source (sometimes referred to hereinafter as lead compound). A leadcompound is preferably soluble in a liquid phase under the reactionconditions. Examples of such lead compounds include, but are not limitedto, lead oxides, for example PbO, Pb₃O₄, and PbO₂; lead carboxylates,for example lead (II) acetate and lead (II) propionate; inorganic leadsalts such as lead (II) nitrate and lead (II) sulfate; alkoxy andaryloxy lead compounds such as lead (II) methoxide, and lead (II)phenoxide; lead complexes such as lead (II) acetylacetonate andphthalocyanine lead, and organolead compounds (that is lead compoundshaving at least one lead-carbon bond) such as tetraethyl lead. Of thesecompounds, lead oxides and lead compounds represented by the formulaPb(OR)₂ wherein R is an aryl group having a carbon number from 6 to 10are preferred. Mixtures of the aforementioned lead compounds are alsocontemplated.

[0039] Examples of cerium sources (sometimes referred to hereinafter ascerium compounds) include cerium carboxylates such as cerium acetate,and cerium salts of β-diketones such as cerium (III) 2,4-pentanedionate(cerium (III) acetylacetonate). Mixtures of cerium compounds may also beemployed. The preferred cerium compounds are cerium 2,4-pentanedionates.

[0040] Examples of titanium sources (sometimes referred to hereinafteras titanium compounds) comprise inorganic titanium salts such astitanium (IV) bromide, titanium (IV) chloride; titanium alkoxides andaryloxides such as titanium (IV) methoxide, titanium (IV) ethoxide,titanium (IV) isopropoxide, titanium (IV) 2-ethylhexoxide, titanium (IV)butoxide, titanium (IV) 2-ethyl-1,3-hexanediolate, titanium (IV)(triethanolaminato)-isopropoxide and titanium(IV) phenoxide; andtitanium salts of β-diketones or β-ketoesters such as titanium (IV)diisopropoxide bis(acetylacetonate), titanium (IV) bis(ethylacetoacetato) diisopropoxide, titanium (IV) oxidebis(2,4-pentanedionate) (or titanium (IV) oxide acetylacetonate).Mixtures of titanium compounds may also be employed. The preferredtitanium compounds are titanium (IV) alkoxides and aryloxides such astitanium (IV) butoxide and titanium (IV) phenoxide; and salts ofβ-diketones or β-ketoesters such as titanium (IV) oxide acetylacetonateand titanium (IV) bis(ethyl acetoacetato)diisopropoxide.

[0041] Examples of copper sources (sometimes referred to hereinafter ascopper compounds) comprise inorganic cupric or cuprous salts or coppercomplexes. Illustrative examples include, but are not limited to, copper(I) chloride, copper (I) bromide, copper (I) iodide; copper (II)chloride, copper (II) bromide, copper (II) iodide; copper carboxylatessuch as copper acetate, copper gluconate, and copper (II)2-ethylhexanoate; copper (II) hydroxide, copper alkoxides andaryloxides; copper nitrate; and copper salts of β-diketones such ascopper (II) bis(2,4-pentanedionate) (or copper (11) acetylacetonate).Mixtures of copper compounds may also be employed. The preferred coppercompounds are 2,4-pentanedionates. Another preferred class of metalco-catalysts comprises a combination of at least one titanium source andat least one copper source.

[0042] In addition to those illustrated above, one or more additionalmetal cocatalysts may be used in the carbonylation catalyst system,provided any additional metal co-catalyst does not deactivate (i.e.“poison”) the original metal co-catalyst or cocatalyst combination, suchthat it loses its effectiveness. A non-exclusive listing of additionalmetal co-catalysts includes iron, ytterbium, zinc, manganese, europium,bismuth, nickel, cobalt, iridium, rhodium, ruthenium, chromium, andyttrium.

[0043] Typically, the at least one metal co-catalyst component C ispresent in the amount of about 0.1-200 gram-atoms, preferably about1-150 gram-atoms, and more preferably about 2-100 gram-atoms of totalmetals in component C per gram-atom of the Group 8, 9, or 10 metal ofcomponent A. Total metals in component C means the combination of allthe metals in component C which may comprise one metal or more than onemetal. In embodiments wherein the metal co-catalyst comprises at leastone copper compound and at least one lead compound, then the mole ratioof copper to lead is about 2-10 moles copper to about 100 moles lead. Inother embodiments when palladium, titanium, and copper are included inthe reaction, the molar ratio of titanium relative to palladium at theinitiation of the reaction is in one embodiment in a range of betweenabout 0.1 and about 150, and the molar ratio of copper relative topalladium is at the initiation of the reaction is in one embodiment in arange of between about 0.1 and about 15. In other embodiments the moleratio of copper to titanium is about 5-20 moles copper to about 2-30moles titanium.

[0044] Component D is at least one activating organic solvent. In oneembodiment the activating organic solvent is at least one polyether;i.e., at least one compound containing two or more C—O—C linkages. Thepolyether is preferably free of hydroxy groups to maximize its desiredactivity and avoid competition with the aromatic hydroxy compound in thecarbonylation reaction.

[0045] The polyether preferably contains two or more (O—C—C) units. Thepolyether may be “aliphatic” or mixed aliphatic-aromatic. As used in theidentification of the polyether, the term “aliphatic” refers to thestructures of hydrocarbon groups within the molecule, not to the overallstructure of the molecule. Thus, “aliphatic polyether” includesheterocyclic polyether molecules containing aliphatic groups withintheir molecular structure. Suitable aliphatic polyethers includediethylene glycol dialkyl ethers such as diethylene glycol dimethylether (hereinafter “diglyme”), triethylene glycol dialkyl ethers such astriethylene glycol dimethyl other (hereinafter “triglyme”),tetraethylene glycol dialkyl ethers such as tetraethylene glycoldimethyl ether (hereinafter “tetraglyme”), polyethylene glycol dialkylethers such as polyethylene glycol dimethyl ether and crown ethers suchas 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane) and 18-crown-6(1,4,7,10,13,16-hexaoxacyclooctadecane). Illustrative mixedaliphatic-aromatic polyethers are diethylene glycol diphenyl ether andbenzo-18-crown-6. In one embodiment of the invention tetraglyme ispreferred.

[0046] In alternative embodiments, the activating organic solvent can bea nitrile. Suitable nitrile promoters for the present method includeC₂₋₈ aliphatic or C₇₋₁₀ aromatic mono- or dinitriles. Illustrativemononitriles include acetonitrile, propionitrile, and benzonitrile.Illustrative dinitriles include succinonitrile, adiponitrile, andbenzodinitrile. Mononitriles are generally preferred; more specificallypreferred is acetonitrile.

[0047] In further alternative embodiments, the activating organicsolvent can be a carboxylic acid amide. Fully substituted amides(containing no NH groups including the amide nitrogen) are preferred.Aliphatic, aromatic or heterocyclic amides may be used. Illustrativeamides are dimethylformamide, dimethylacetamide (hereinafter sometimes“DMA”), dimethylbenzamide and N-methylpyrrolidinone (NMP). Particularlypreferred are NMP and DMA.

[0048] The activating organic solvent can also be a sulfone, which maybe aliphatic, aromatic or heterocyclic. Illustrative sulfones aredimethyl sulfone, diethyl sulfone, diphenyl sulfone and sulfolane(tetrahydrothiophene- 1,1-dioxide). Of these, sulfolane is oftenpreferred.

[0049] It is noted that the function of the activating organic solvent,component D, in the present invention is not that of an inert solvent.Rather, the activating organic solvent is an active catalyst componentthat improves the yield of or selectivity toward the aromatic carbonate.The role of the activating organic solvent, when present, is believed tobe to increase the degree of dissociation and ionization of salt ofcomponent B, such as sodium bromide, perhaps by forming a complex withthe cationic portion of said component, although the invention is in noway dependent on this or any other theory of operation. The amount ofcomponent D employed will be an amount effective to optimize diarylcarbonate formation, in general by increasing the yield of the desireddiaryl carbonate as evidenced, for example, by an increase in “turnovernumber”; i.e., the number of moles of diaryl carbonate formed pergram-atom of the Group 8, 9, or 10 metal catalyst component present.This amount is most often about 1-60% by volume, preferably about 1-25%by volume, more preferably about 2-15% by volume, still more preferablyabout 4-12% by volume, and yet still more preferably about 6-8% byvolume based on the total of aromatic hydroxy compound and component D.

[0050] The amount of activating organic solvent component D may,however, typically depend to some extent on the salt component B and thecomplexing ability of the organic compound employed. Crown ethers, forexample, have a very high complexing tendency with metal cations. Forexample, 15-crown-5 complexes efficiently with sodium and 18-crown-6with potassium. Such compounds may be used in amounts as low as anequimolar amount based on salt component B. Other compounds useful ascomponent D, such as straight chain polyethers (e.g., diglyme), may beoptimally effective at much higher levels. The preferred proportion ofany specific material used as activating organic solvent component D canbe determined by simple experimentation.

[0051] At least one base (component E) may optionally be present in thereaction mixture. Any effective bases or mixtures thereof, whetherorganic or inorganic may be used in the process of the invention. Inpreferred embodiments a base is used which is capable of generating theconjugate base of an aromatic hydroxy compound and not interfering withthe function of any catalyst component. Illustrative examples ofinorganic bases include, but are not limited to, alkali metal hydroxidesand alkali metal carbonates, alkali metal carboxylates or other salts ofweak acids or alkali metal salts of aromatic hydroxy compounds, forexample alkali metal phenoxides. Obviously, the hydrates of alkali metalphenoxides can also be used in the process. An example of such a hydratewhich may be mentioned is sodium phenoxide trihydrate. In general theuse of hydrates and the concomitant addition of water to the reactionmixture may lead, inter alia, to poorer conversion rates anddecomposition of carbonates formed. Illustrative examples of organicbases include, but are not limited to, onium hydroxides, oniumphenoxides, ammonium hydroxides, ammonium phenoxides, phosphoniumhydroxides, phosphonium phenoxides, sulfonium hydroxides, sulfoniumphenoxides, guanidinium hydroxides, guanidinium phenoxides, tertiaryamines which bear as organic radicals C₆-C₁₀ aryl, C₆-C₁₂ aralkyl and/orC₁-C₂₀-alkyl or represent pyridine bases or hydrogenated pyridine bases;for example dimethylbutylamine, triethylamine, tripropylamine,tributylamine, trioctylamine, benzyldimethylamine, dioctylbenzylamine,dimethylphenethylamine, 1 -dimethylamino-2-phenylpropane, pyridine,N-methylpiperidine, 1,2,2,6,6-pentamethylpiperidine. The base used ispreferably an alkali metal salt of an aromatic hydroxy compound,particularly preferably an alkali metal salt of the aromatic hydroxycompound which is also to be converted to the organic carbonate. Thesealkali metal salts can be lithium salts, sodium salts, potassium salts,rubidium salts or cesium salts. Lithium phenoxide, sodium phenoxide andpotassium phenoxide are preferably used; sodium phenoxide isparticularly preferred.

[0052] A base may be added as a pure compound or as a precursorcompound, such as addition of an alkali metal-comprising base as aprecursor for an alkali metal salt of the aromatic hydroxy compoundwhich is also to be converted to the organic carbonate. Illustrativealkali metal-comprising bases include, but are not limited to, sodiumhydroxide, and sodium salts of weak acids such as sodium carboxylates,sodium acetate, and sodium acetylacetonate. A base may be added to thereaction mixture in any convenient form, such as in solid form or as aliquid or a melt, either in neat form or in a solution. In a furtherembodiment of the invention, the base is added to the reaction mixtureas a solution which contains about 0.1 to about 80% by weight,preferably about 0.5 to about 65% by weight, particularly preferablyabout 1 to about 50% by weight of the base. The solvents which mayoptionally be used here are both alcohols or phenols, such as the phenolto be reacted, and inert solvents. Examples of solvents which may bementioned are dimethylacetamide, N-methylpyrrolidinone, dioxane,t-butanol, cumyl alcohol, isoamyl alcohol, tetramethylurea, diethyleneglycol, halogenated hydrocarbons (e.g. chlorobenzene or dichlorobenzene)and ethers, such as tetraethylene glycol dimethyl ether. The solventsmay be used alone or in any combination with each other.

[0053] A base, if used, is added in an amount independent of thestoichiometry. The ratio of base to Group 8, 9, or 10 metal having anatomic number of at least 44 is preferably chosen in such a way that atleast one base is present in an amount in a range of about 0.1 to about2500, preferably about 5 to about 1500, more preferably about 50 to1000, and still more preferably about 100 to 400 molar equivalents ofbase based on component A.

[0054] The oxidative carbonylation reaction can be carried out in abatch reactor, or a semi-continuous, or continuous reactor systemcomprising one or more reaction vessels. Reaction vessels suitable foruse in the process according to the invention with either homogeneous orheterogeneous catalysts include stirrer vessels, autoclaves and bubblecolumns, it being possible for these to be employed as individualreactors or as a cascade. In a cascade 2 to 15, preferably 2 to 10, andparticularly preferably 2 to 5, reactors may be connected in series.

[0055] The method of the invention is preferably conducted in at leastone reaction vessel in which the aromatic hydroxy compound, catalystsystem, and any other components are charged to a reactor, pressurizedunder carbon monoxide and oxygen, and heated. The reaction pressure ismost often in a range of about 0.1-51 megapascals, preferably about0.3-25 megapascals, more preferably about 1.0-17 megapascals and stillmore preferably about 1.1-15 megapascals. Gas is usually supplied inproportions of about 1-50 mole percent oxygen with the balance beingcarbon monoxide. Additional gases may be present in amounts that do notdeleteriously affect the carbonylation reaction. The gases may beintroduced separately or as a mixture. Reaction temperatures in therange of about 30-210° C. and preferably about 50-160° C. are typical,with temperatures in the range of about 80-125° C. being more preferred.Agitation of the reaction mixture in at least one reaction vessel ispreferably employed to aid the reaction. Agitation may be performed byany known method, including at least one of stirring or gas sparging.

[0056] In order for the reaction to be as rapid as possible, it ispreferred to substantially maintain the total gas pressure and partialpressure of carbon monoxide and oxygen until a desired conversion levelof aromatic hydroxy compound is achieved, as described, for example, inU.S. Pat. No. 5,399,734, which is incorporated herein by reference.

[0057] The diaryl carbonates produced by this method may be recovered atany convenient point in the process loop and isolated by conventionaltechniques. It is often preferred to form and thermally crack an adductof the diaryl carbonate with the hydroxy aromatic compound, as isdescribed in U.S. Pat. Nos. 5,239,106 and 5,312,955, which areincorporated herein by reference.

[0058] Water removal in an integrated process for oxidativecarbonylation of aromatic hydroxy compounds may be illustrated withreference to the flow diagrams of FIGS. 1, 2, and 3. In FIG. 1 at leastone reaction vessel (1) has contents comprising aromatic hydroxycompound and catalyst system under pressure of carbon monoxide andoxygen. The reactor contents may be agitated by known means; in theembodiment in FIG. 1 agitation is illustrated by stirrer (4). Carbonmonoxide, oxygen, and optional other gas may be fed to a reactor (1)through one or more gaseous feed inlets; in the embodiment in FIG. 1 asingle gaseous feed inlet (5) is illustrated. Catalyst and liquid (forexample, aromatic hydroxy compound) may be fed to a reactor (1) via oneor more feed inlets; in the embodiment in FIG. 1 a single feed inlet (6)is illustrated. A liquid stream to be dried may be removed from reactionvessel (1) via an outlet (7) for transfer to a first disengagementvessel (2). The amount of liquid stream withdrawn per hour may amount toabout 0.01 to 30 times, preferably about 0.05 to 20 times, andparticularly preferably about 0.1 to 10 times, the contents of thereactor.

[0059] Removal of a liquid stream may be performed by any convenientmethod, preferably by gravity or pump or a combination thereof. As shownin an embodiment in FIG. 1 a liquid stream may be removed from reactionvessel (1) when the liquid level of reaction mixture reaches a levelequivalent to the highest level of outlet (7). Thus, in one embodimentas material is continuously pumped into reaction vessel (1) acorresponding flow of material may transfer continuously todisengagement vessel (2) via outlet (7). In alternative embodiments theliquid level in reaction vessel (1) may go temporarily over the highestlevel of outlet (7) by temporarily closing outlet (7). In yet otheralternative embodiments the liquid level in reaction vessel (1) may betemporarily below the highest level of outlet (7) and transfer todisengagement vessel (2) may be performed by pump. The exact mode ofoperation at a particular time offers beneficial alternatives and maydepend on such factors as the degree of conversion of aromatic hydroxycompound to diarylcarbonate under the particular process conditions.

[0060] Disengagement vessel (2) is not agitated. Not agitated means thatno deliberate means of agitation is employed other than adventitiousagitation, such as that which may occur when a liquid stream istransferred to or from disengagement vessel (2). By maintaining theliquid stream in disengagement vessel (2) without agitation, gases whichhad been entrained by agitation in reaction vessel (1) may escape fromthe liquid stream.

[0061] The liquid stream in disengagement vessel (2) may be at apressure in a range of between about atmospheric pressure and thepressure in reaction vessel (1). In some embodiments the liquid streamin disengagement vessel (2) may be at a pressure which is lower thanthat in reaction vessel (1). In one embodiment the liquid stream indisengagement vessel (2) is at essentially the same pressure as thereaction mixture in reaction vessel (1). In another embodiment theliquid stream in disengagement vessel (2) is at essentially the sametemperature and pressure as the reaction mixture in reaction vessel (1).

[0062] Although the invention is in no way dependent upon mechanism, itis believed that without agitation oxygen dissolved in the liquid steamin disengagement vessel (2) may be consumed through reaction leaving ahigh concentration of dissolved carbon monoxide. A high concentration ofcarbon monoxide and also possibly high temperature in the absence ofsufficient oxygen may be detrimental to catalyst activity and lifetimedepending upon catalyst composition. The catalyst system must be able towithstand the process sequence, particularly the gas disengagement atthe reaction temperature and pressure, such that when it is returned tothe reactor following removal of water the catalyst activity ismaintained or minimally reduced. It has been unexpectedly found thatsome catalyst packages do not survive this process at high temperature,and the temperature may need to be lowered for these systems prior toremoval of water in flash vessel (3) under reduced pressure. Inparticular it has been discovered that a catalyst system containing leadand a tetraalkylammonium halide does not retain its activity unless thetemperature is lowered prior to removal of water in flash vessel (3).Unexpectedly a catalyst system comprising copper and titanium and analkali metal halide has been found to retain its activity under the sameconditions and does not require lowering of temperature or pressureprior to removal of water.

[0063] Outlet gases (13) from reaction vessel (1) and disengagementvessel (2) are recycled using standard methods. Typically outlet gasesare cooled to condense and remove water and other condensable compoundsbefore reuse of gases.

[0064] In one embodiment of the water removal process a liquid streamfrom disengagement vessel (2) is transferred via outlet (8) to at leastone flash vessel (3). A flash vessel for evaporation of water may be anytype of apparatus known to those skilled in the art for this purpose.For example, a flash vessel may comprise vertical-pipe, horizontal-pipe,slanting-pipe, rotor or thin-layer, centrifugal, worm and falling-filmevaporators, tube-bundle evaporators, basket evaporators, evaporatorswith external return pipe and forced circulation, evaporators withexternal heating elements and forced circulation and other evaporatorsknown to those skilled in the art. Furthermore, simple distillation andrectifing columns with accompanying heating elements are also suitable;preferably a flash vessel comprises thin-layer and falling-filmevaporators and evaporators with forced circulation and heating elementslocated internally or externally.

[0065] Flash vessel (3) may represent a single flash vessel or more thanone flash vessel, each with at least one stage. In one embodiment atleast one flash vessel has more than one stage, for example two or threestages. The liquid stream from disengagement vessel (2) can betransferred continuously, semi-continuously (for example, periodically),or in a batch which essentially empties all of disengagement vessel (2).If desired, the temperature of the liquid stream portion removed fromdisengagement vessel (2) may be lowered from the temperature of theinitial reaction mixture by cooling disengagement vessel (2) or throughheat exchange during transfer from outlet (8), or both. When thetemperature is lowered, it is typically lowered to a temperature in arange between about 50° C. and about 90° C.

[0066] In flash vessel (3) the liquid stream portion is subjected to areduced pressure in that the pressure is lower than the pressure inreaction vessel (1). Typically the reduced pressure is in the range ofabout 0.1-500 kilopascals, preferably about 0.753 kilopascals, morepreferably about 0.7-40 kilopascals, still more preferably about 0.7-13kilopascals, and yet still more preferably about 2-7 kilopascals, and atemperature in the range of about 50-160° C. for removal of a majorityof the water and varying amounts of aromatic hydroxy compound and anyother volatile constituents through outlet (9). Because entrained gaseshave escaped from the liquid stream in disengagement vessel (2), lessaromatic hydroxy compound is entrained and lost from flash vessel (3)when the liquid stream from (8) undergoes pressure drop in flash vessel(3). In the present context majority of water means greater than about50% by weight, preferably about 50-99% by weight, and more preferablyabout 50-80% by weight of water in the liquid stream initially.

[0067] Generally, the temperature and pressure in flash vessel (3) aresuch as to keep the liquid stream portion molten without degrading thecatalyst. Volatile material exiting flash vessel (3) through outlet (9)may be sent for recovery and recycle of aromatic hydroxy compound andoptional other volatile constituents. The removal of water in flashvessel (3) may be performed under essentially isothermal conditionsthrough supplying heat to flash vessel (3), or the removal of water inflash vessel (3) may be performed under essentially adiabaticconditions. In another embodiment the removal of water in flash vessel(3) may be performed at a temperature lower than that of the feedtemperature from outlet (8) but higher than that resulting fromadiabatic operation by supplying a lower amount of heat to flash vessel(3) than in the isothermal process. In various embodiments the removalof water in flash vessel (3) may be performed in one embodiment at atemperature which is greater than 30° C. higher than the temperature inthe reaction vessel (1); and in another embodiment at a temperaturewhich is at least 35° C. higher than the temperature in the reactionvessel (1). In other embodiments the removal of water in flash vessel(3) may be performed in one embodiment at a temperature which is greaterthan 30° C. lower than the temperature in the reaction vessel (1); andin another embodiment at a temperature which is at least 35° C. lowerthan the temperature in the reaction vessel (1). In one embodiment driedliquid stream from flash vessel (3) maybe withdrawn through outlet (10)and separated into a stream (11) for recovery and isolation of diarylcarbonate and any catalyst constituents, and a stream (12) for recycleof dried reaction mixture to the reaction vessel (1). Optionally, atleast one holding vessel, or at least one filtration device for solidremoval, or both may be present between flash vessel (10) and reactionvessel (1). The ratio of stream (11) for recovery and stream (12) forrecycle to reaction vessel (1) is in a range of about 0.1-30 andpreferably in a range of about 0.5-15. Optionally, make-up aromatichydroxy compound and optional other volatile constituents and make-upcatalyst constituents may be added to a reaction vessel (1) or to aliquid stream at some point in the process loop before return toreaction vessel (1), or both. In one embodiment make-up aromatic hydroxycompound and optional other volatile constituents and make-up catalystconstituents are added to a dried liquid stream returning to a reactionvessel.

[0068] In another embodiment of the invention FIG. 2 shows a flowdiagram for an embodiment of the process that is essentially identicalin equipment and operation to the process described in the flow diagramof FIG. 1, with the exception that a second disengagement vessel (14) isincluded between a first disengagement vessel (2) and flash vessel (3).The second disengagement vessel (14) is maintained at lower pressurethan the first disengagement vessel. In preferred embodiments the seconddisengagement vessel (14) is maintained at essentially atmosphericpressure, more preferably at slightly above atmospheric pressure, andstill more preferably at a pressure in a range of between about 102 andabout 345 kilopascals. A liquid stream in second disengagement vessel(14) at atmospheric pressure experiences loss of dissolved gases when aliquid stream experiences the lower pressure in a second disengagementvessel (14) compared to the pressure in first disengagement vessel (2).A liquid stream from second disengagement vessel (14) is sent to flashvessel (3) through an outlet (16) and treated in the same manner asdescribed for the process in FIG. 1. Because dissolved gases haveescaped from the liquid stream in second disengagement vessel (14), lessaromatic hydroxy compound is entrained and lost from flash vessel (3)when the liquid stream from (16) undergoes pressure drop in flash vessel(3). Another advantage is that less capacity from the vacuum pumpattached to the evaporation unit is required, and it is easier to get tolow pressures in the evaporation unit.

[0069] Dissolved gases which escape from a liquid stream through outlet(15) from second disengagement vessel (14) are recycled using standardmethods. Typically outlet gases are cooled to condense and remove waterand other condensable compounds before reuse of gas.

[0070] One of the advantages of the embodiments of the inventionillustrated in FIGS. 1 and 2 is that in various embodiments there is norequirement to depressurize the gas in order to separate it from theliquid prior to the flash operation. Thus, gas recompression costs maybe minimized. In addition, the water removal process described herein ismore economically viable than using molecular sieves for drying reactionmixtures producing products in which water is deleterious to the processand/or products produced therefrom.

[0071] In still another embodiment of the invention FIG. 3 shows a flowdiagram for a process that is essentially identical in equipment andoperation to the process described in the flow diagram of FIG. 1, withthe exception that no disengagement vessel is present between a reactionvessel (1) and a flash vessel (3). In this embodiment a liquid stream tobe dried may be removed from a reaction vessel via an outlet (7) fortransfer to a flash vessel (3). Removal of liquid stream may beperformed by any convenient method, preferably by pressuredifferentiation or pump, or a combination thereof. As shown in anembodiment in FIG. 3 a liquid stream may be removed from reaction vessel(1) and transferred to flash vessel (3) where it undergoesdepressurization and removal of water under the reduced pressureconditions of flash vessel (3) in the same manner as described for theoperation of flash vessel (3) in FIG. 1. In one embodiment, followingremoval of water, a dried liquid stream from flash vessel (3) may bewithdrawn through outlet (10) and separated into a stream (11) forrecovery and isolation of diaryl carbonate and any catalystconstituents, and a stream (12) for recycle of dried reaction mixture tothe reaction vessel (1), again in the same manner as described in theembodiment illustrated in FIG. 1.

[0072] One of the advantages of the embodiments of the inventionillustrated in FIG. 3 is that there is no requirement to disengage thegas from the liquid prior to the flash operation. In addition, the waterremoval process described herein is more economically viable than usingmolecular sieves for drying reaction mixtures producing products inwhich water is deleterious to the process and/or products producedtherefrom.

[0073] In the various embodiments of the invention the reduction of thepressure of a liquid stream taken from a reaction vessel (1) to thepressure of a flash vessel (3) may be done in either a single stage orin more than one stage. In some embodiments such as may be illustratedin certain embodiments in FIG. 3 the reduction in pressure of a liquidstream is done in a single stage. In other embodiments such as may beillustrated in certain embodiments in FIGS. 1 and 2 the reduction inpressure of a liquid stream may be done in one or more stages. In aparticular embodiment the reduction in pressure of a liquid stream maybe done in two to five stages between a reaction vessel (1) and a flashvessel (3).

[0074] In a preferred embodiment water removal in the integrated processfor oxidative carbonylation of aromatic hydroxy compounds is continuous.When equilibrium is attained in the process, water levels in the atleast one reaction vessel are typically at essentially a constant levelof about 1000-10,000 ppm, and preferably about 2000-5000 ppm. Waterlevels in the dried liquid stream portion exiting flash vessel (3) aretypically about 50-2000 ppm, and preferably about 250-1000 ppm.

[0075] Diaryl carbonates produced by the method may be recovered andisolated at any convenient point in the process loop. In variousembodiments at least a portion of diaryl carbonate is recovered fromdried liquid stream. In other embodiments at least a portion of diarylcarbonate is recovered from a liquid stream before drying. In oneembodiment at least a portion of diaryl carbonate is recovered from aliquid stream taken directly from a reactor and before drying. Inanother embodiment at least a portion of diaryl carbonate is recoveredfrom at least a portion of a liquid stream taken directly from a reactorand before drying. In still other embodiments at least a portion ofdiaryl carbonate may be recovered from streams taken from at least twopoints in a process loop.

[0076] Embodiments of the invention are illustrated by the followingnon-limiting examples.

EXAMPLE 1

[0077] A reaction was run at 100° C. using a catalyst consisting ofpalladium acetylacetonate (15 ppm), copper (II) acetylacetonate(Cu(acac)₂; 5 equivalents versus Pd), titanium (IV) oxideacetylacetonate (TiO(acac)₂; 15 equivalents versus Pd), sodium bromide(791 equivalents versus Pd), in the presence of reactant phenol andsolvent tetraglyme (tetraethylene glycol dimethyl ether, 7% by volume).Gases used were a mixture of carbon monoxide (91 mole %) and oxygen (9mole %) at about 12.4 megapascals. Molecular sieves (30 grams, type 3A)were placed in a perforated TEFLON basket mounted on the stir shaft justabove the impeller. After one hour, the reactor was depressurized,allowed to stir at ambient pressure for 10 minutes, and thenre-pressurized at 100° C., and the reaction was continued. The amount ofdiphenyl carbonate (DPC) product obtained at progressive time points isshown in FIG. 4. Also shown on the same plot is the DPC obtained in arun obtained under the same conditions, but with no interruption of thereaction by depressurization during the progress of the reaction. Thedata relating to the run in which the reaction was interrupted bydepressurization does not include the period when the reactor wasdepressurized (after one hour, for 10 minutes). FIG. 4 shows that thedepressurization did not adversely affect the catalyst.

COMPARATIVE EXAMPLE 1A

[0078] A reaction was run at 100° C. using a catalyst consisting ofpalladium acetylacetonate (15 ppm), lead (II) oxide (56 equivalentsversus Pd), and tetraethyl ammonium bromide (810 equivalents versus Pd),in the presence of reactant phenol. Gases used were a mixture of carbonmonoxide (91%) and oxygen (9%) at about 12.4 megapascals. Molecularsieves (30 grams, type 3A) were placed in a perforated TEFLON basketmounted on the stir shaft just above the impeller. After 60 minutes thesystem was depressurized at the reaction temperature (100° C.) for 10minutes, and then repressurized. The amount of diphenyl carbonate (DPC)product obtained at progressive time points are shown in FIG. 5. Alsoshown on the same plot is the DPC obtained from a run under the sameconditions, but with no interruption of the reaction by depressurizationduring the progress of the reaction. The data relating to the run inwhich the reaction was interrupted by depressurization does not includethe period when the reactor was depressurized (after one hour, for 10minutes). FIG. 5 shows that the depressurization affected the catalystperformance adversely, making this catalyst suitable in a water removalprocess under conditions where the temperature is lowered before thedepressurization is performed.

COMPARATIVE EXAMPLE 1B

[0079] A reaction was run at 100° C. and about 9.3 megapascals using acatalyst consisting of palladium acetylacetonate (25 ppm), lead (II)oxide (56 equivalents versus Pd), tetraethylammonium bromide (600equivalents versus Pd), in the presence of reactant phenol. Gases usedwere a mixture of carbon monoxide (91%) and oxygen (9%). Molecularsieves (30 grams, type 3A) were placed in a perforated TEFLON basketmounted on the stir shaft just above the impeller. After 30 minutes thesystem was cooled to 60° C. and then depressurized, and stirred atambient pressure for 36 minutes, and then repressurized at 60° C. to thereaction pressure, and then re-heated to the reaction temperature (100°C.). The amounts of diphenyl carbonate (DPC) product obtained atprogressive time points are 6.8% by weight DPC at 0.5 hours (prior todepressurization), 11.3% after reattaining reaction temperature afterrepressurization, and 18.3% and 23.7% after two subsequent 30 minuteperiods. The significant amount of DPC obtained after thedepressurization-repressurization sequence at 60° C. (instead of at thereaction temperature (100° C.) indicates that the catalyst retains itsactivity after the depressurization at 60° C.

EXAMPLE 2

[0080] A reaction was run at 100° C. and about 10.3 megapascals using 15ppm palladium as palladium acetylacetonate, 13 equivalents (versus Pd)of copper as Cu(acac)₂, 27 equivalents (versus Pd) of titanium asTiO(acac)₂, 429 equivalents (versus Pd) of sodium bromide, 805equivalents (versus Pd) of sodium hydroxide, with tetraglymeconstituting 7 volume % of the initial reaction mass, and no molecularsieves. The reaction was stopped after 50 minutes by stopping stirring,depressurizing to atmospheric pressure (requiring 1 minute), and thenafter an additional 1.5 minutes, cooling the reactor to 60° C. Thecontents were removed and put into a rotary evaporator at about 60° C.,where about 10 grams (g) material were evaporated. The contents wereremoved from the rotary evaporator, and phenol make-up was added toaccount for the mass removed during the rotary evaporation process,after which the contents were re-introduced into the reactor and thereaction resumed at about 10.3 megapascals and 100° C. for 30 minutes.The reaction was then stopped by stopping stirring, depressurizing toatmospheric pressure (requiring 1 minute), and then after an additional1.5 minutes, cooling the reactor to 60° C. The contents were put into arotary evaporator as before, and about 21 grams were evaporated, andphenol make-up was again added to account for the removed mass beforeresuming the reaction. The reaction was then permitted to run until atotal of 2.33 hours of reaction had occurred. The initial total mass ofreactants and catalyst (not including gases) was 99.53 grams. After 2.33hours of reaction, there was 25.2% by weight of DPC as determined byhigh performance liquid chromatography (HPLC).

EXAMPLE 3

[0081] A reaction was run at about 10.3 megapascals at 100° C. using 14ppm palladium as palladium acetylacetonate, 20 equivalents (versus Pd)of copper as Cu(acac)₂, 27 equivalents (versus Pd) of titanium asTiO(acac)₂, 423 equivalents (versus Pd) of sodium bromide, 852equivalents (versus Pd) of base (sodium hydroxide), with tetraglymeconstituting 7% by volume of the initial reaction mass, and no molecularsieves. Gases used were a mixture of carbon monoxide (91%) and oxygen(9%). The reaction was stopped after 30 minutes by cooling the reactorto 60° C., and then depressurizing, and the contents were removed andput into a rotary evaporator at about 60° C., where about 32 grams (g)material were evaporated. The contents were removed from the rotaryevaporator, and phenol make-up was added to account for the mass removedduring the rotary evaporation process, after which the contents werere-introduced into the reactor and the reaction resumed at about 10.3megapascals and 100° C for 30 minutes. The reactor was then cooled to60° C. and depressurized, and the contents were put into a rotaryevaporator as before, and about 19 grams were evaporated, and phenolmake-up was again added to account for the removed mass before resumingthe reaction. The reaction was then permitted to run until a total of2.05 hours of reaction had occurred.

[0082] The initial total mass of reactants and catalyst (not includinggases) was 98.46 grams. After 2.05 hours of reaction, there was 26.1% byweight of DPC as determined by high performance liquid chromatography(HPLC).

COMPARATIVE EXAMPLE 3A

[0083] A reaction was run using 14 ppm palladium as palladiumacetylacetonate, 20 equivalents (versus Pd) of copper as Cu(acac)₂, 27equivalents (versus Pd) of titanium as TiO(acac)₂, 801 equivalents(versus Pd) of sodium bromide, 452 equivalents (versus Pd) of base(sodium hydroxide), with tetraglyme constituting 7% by volume of theinitial reaction mass, and 30 g of molecular sieves (type 3A). Gasesused were a mixture of carbon monoxide (91%) and oxygen (9%). Thereaction was run at about 12.4 megapascals at 100° C. until a total of2.5 hours of reaction had occurred.

[0084] The initial total mass of reactants and catalyst (not includinggases) was 64.52 grams. After 2.5 hours of reaction there was 29.2% byweight of DPC present in the reaction mixture as determined by HPLC.

COMPARATIVE EXAMPLE 3B

[0085] A reaction was run using 14 ppm palladium as palladiumacetylacetonate, 20 equivalents (versus Pd) of copper as Cu(acac)₂, 27equivalents (versus Pd) of titanium as TiO(acac)₂, 424 equivalents(versus Pd) of sodium bromide, 852 equivalents (versus Pd) of base(sodium hydroxide), with tetraglyme constituting 7% by volume of theinitial reaction mass, and no molecular sieves. Gases used were amixture of carbon monoxide (91%) and oxygen (9%). The reaction was runat about 12.4 megapascals at 100° C. until a total of 2.5 hours ofreaction had occurred.

[0086] The initial total mass of reactants and catalyst (not includinggases) was 99.86 grams. After 1, 1.5, 2, and 2.5 hours of reaction therewas 13.0%, 12.8%, 11.6%, and 10.6% by weight of DPC, respectively, asdetermined by HPLC.

[0087] Comparison of example 3 with comparative example 3B shows theimprovement obtained from water removal (example 3) versus not usingwater removal (comparative example 3B). Comparison of example 3 withcomparative example 3A shows that the evaporative method providescomparable improvement in the reaction performance versus the molecularsieve method for water removal.

EXAMPLE 4 AND COMPARATIVE EXAMPLES 4A AND 4B

[0088] Reactions are run similar to examples 3 and comparative examples3A and 3B except that a lead source is employed as inorganicco-catalyst. Comparison of example 4 with comparative example 4B showsan improvement in DPC yield obtained from water removal (example 4)versus not using water removal (example 4B). Comparison of example 4with comparative example 4A shows that the evaporative method providescomparable improvement in DPC yield versus the molecular sieve methodfor water removal.

EXAMPLE 5 AND COMPARATIVE EXAMPLES 5A AND 5B

[0089] Reactions are run as in examples 1 and comparative examples 1Aand 1B except that a combination of lead source and titanium source isemployed as inorganic co-catalyst. Comparison of example 5 withcomparative example 5B shows an improvement in DPC yield obtained fromwater removal (example 5) versus not using water removal (example 5B).Comparison of example 5 with comparative example 5A shows that theevaporative method provides comparable improvement in DPC yield versusthe molecular sieve method for water removal.

EXAMPLE 6 AND COMPARATIVE EXAMPLES 6A AND 6B

[0090] Reactions are run as in examples 1 and comparative examples 1Aand 1B except that a combination of lead source and copper source isemployed as inorganic co-catalyst. Comparison of example 6 withcomparative example 6B shows an improvement in DPC yield obtained fromwater removal (example 6) versus not using water removal (example 6B).Comparison of example 6 with comparative example 6A shows that theevaporative method provides comparable improvement in DPC yield versusthe molecular sieve method for water removal.

EXAMPLE 7 AND COMPARATIVE EXAMPLES 7A AND 7B

[0091] Reactions are run as in examples 1 and comparative examples 1Aand 1B except that a combination of lead source and cerium source isemployed as inorganic co-catalyst. Comparison of example 7 withcomparative example 7B shows an improvement in DPC yield obtained fromwater removal (example 7) versus not using water removal (example 7B).Comparison of example 7 with comparative example 7A shows that theevaporative method provides comparable improvement in DPC yield versusthe molecular sieve method for water removal.

[0092] While typical embodiments have been set forth for the purpose ofillustration, the foregoing descriptions and examples should not bedeemed to be a limitation on the scope of the invention. Accordingly,various modifications, adaptations, and alternatives may occur to oneskilled in the art without departing from the spirit and scope of thepresent invention.

What is claimed is:
 1. A method for preparing a diaryl carbonate whichcomprises contacting at least one aromatic hydroxy compound with oxygenand carbon monoxide in the presence of an amount effective forcarbonylation of a catalyst composition comprising the following and anyreaction products thereof: (A) at least one Group 8, 9, or 10 metalhaving an atomic number of at least 44 or a compound thereof; (B) atleast one alkali metal salt; (C) at least one metal co-catalyst; (D) atleast one activating organic solvent; and (E) optionally, at least onebase, wherein reaction water is removed by a process comprising thesteps of: (i) removing a liquid stream from an oxidative carbonylationreaction mixture in a reaction vessel; (ii) transferring the liquidstream to a flash vessel wherein the liquid stream to subjected toreduced pressure, whereby a majority of the water is removed; (iii)returning at least a portion of a dried liquid stream to the reactionvessel; and (iv) optionally adding at least one of make-up aromatichydroxy compound or other volatile constituent or catalyst component tothe reaction vessel or to the dried liquid stream before return to thereaction vessel, wherein at least a portion of diaryl carbonate isrecovered from a liquid stream either before or after water removal. 2.The method according to claim 1 wherein the aromatic hydroxy compound isphenol.
 3. The method according to claim 1 wherein the at least oneGroup 8, 9, or 10 metal in component A is palladium.
 4. The methodaccording to claim 3 wherein the at least one palladium source isselected from the group consisting of palladium, palladium black,supported palladium, palladium/carbon, palladium/alumina,palladium/silica, inorganic palladium salts, palladium chloride,palladium bromide, palladium iodide, palladium sulfate, palladiumnitrate, organic palladium salts, palladium acetate, palladium oxalate,palladium (II) acetylacetonate, palladium complexes, PdCl₂(PhCN)₂, andPdCl₂(PPh₃)₂.
 5. The method according to claim 1 wherein the at leastone alkali metal salt of component B is at least one salt selected fromthe group consisting of halides, chloride, bromide, tetrafluoroborate,and hexafluorophosphate.
 6. The method according to claim 5 whereincomponent B is at least one chloride or bromide salt.
 7. The methodaccording to claim 6 wherein component B is an alkali metal bromide. 8.The method according to claim 6 wherein component B is an alkali metalchloride.
 9. The method according to claim 1 wherein the co-catalyst (C)is at least one compound of lead, cerium, copper, or titanium, ormixtures thereof.
 10. The method according to claim 1 wherein the atleast one activating organic solvent is selected from the groupconsisting of polyethers, nitriles, carboxylic acid amides, andsulfones.
 11. The method according to claim 10 wherein the activatingorganic solvent is at least one member selected from the groupconsisting of diethylene glycol dialkyl ether, triethylene glycoldialkyl ether, tetraethylene glycol dialkyl ether, polyethylene glycoldialkyl ether, 15-crown-5, 18-crown-6; acetonitrile;N-methylpyrrolidinone, dimethylacetamide; and sulfolane.
 12. The methodaccording to claim 11 wherein the activating organic solvent istetraethylene glycol dimethyl ether.
 13. The method according to claim 1wherein component A is present in the amount of about 1 gram-atom ofmetal per 800-1,000,000 moles of aromatic hydroxy compound; component Bis present in the amount of about 1-2,000 moles per gram-atom of theGroup 8, 9, or 10 metal of component A; component C is present in theamount of about 0.1-200 gram-atoms of total metals per gram-atom of theGroup 8, 9, or 10 metal of component A; and component D is present in anamount of about 1-60% by volume based on the total volume of aromatichydroxy compound and component D.
 14. The method according to claim 1wherein at least one base, component E, is present in an amount in arange of about 0.1 to 5000 equivalents based on component A.
 15. Themethod according to claim 14 wherein the base is at least one alkalimetal hydroxide, onium hydroxide, alkali metal phenoxide, oniumphenoxide, guanidinium hydroxide or guanidinium phenoxide.
 16. Themethod according to claim 15 wherein the base is at least one alkalimetal hydroxide or alkali metal phenoxide.
 17. The method according toclaim 16 wherein the base is at least one of sodium hydroxide or sodiumphenoxide.
 18. The method according to claim 1 wherein the proportion ofoxygen is about 1-50 mole percent based on total oxygen and carbonmonoxide.
 19. The method according to claim 1 wherein the pressure is ina range of about 0.1-51 megapascals and the temperature is in a range ofabout 50-160° C. in the reaction vessel.
 20. The method according toclaim 1 wherein the temperature of the liquid stream taken from thereaction vessel is maintained at about the temperature of the reactionmixture from which the stream was taken before the liquid stream issubjected to reduced pressure.
 21. The method according to claim 20wherein the temperature is about 50-160° C.
 22. The method according toclaim 1 wherein the temperature of the liquid stream taken from thereaction vessel is lowered from the temperature of the reaction mixturefrom which the stream was taken before the liquid stream is subjected toreduced pressure.
 23. The method according to claim 22 wherein thetemperature is about 50-90° C.
 24. The method according to claim 1wherein the pressure is in a range of about 0.7-53 kilopascals and thetemperature is in a range of about 50-160° C. in the flash vessel. 25.The method according to claim 24 wherein removal of water in the flashvessel is performed under essentially isothermal conditions.
 26. Themethod according to claim 24 wherein removal of water in the flashvessel is performed under essentially adiabatic conditions.
 27. Themethod according to claim 24 wherein removal of water in the flashvessel is performed under conditions between those of adiabatic andisothermal.
 28. The method according to claim 24 wherein removal ofwater in the flash vessel is performed at a temperature which is greaterthan 30° C. higher than the temperature in the reaction vessel.
 29. Themethod according to claim 24 wherein removal of water in the flashvessel is performed at a temperature which is greater than 30° C. lowerthan the temperature in the reaction vessel.
 30. The method according toclaim 1 which further comprises the step of transferring a liquid streamfrom the reaction vessel to a first disengagement vessel before transferof liquid stream to the flash vessel, wherein the first disengagementvessel is not agitated.
 31. The method according to claim 30 wherein thereaction vessel and the first disengagement vessel are at essentiallythe same pressure and temperature.
 32. The method according to claim 30which further comprises the step of transferring the liquid stream fromthe first disengagement vessel to a second disengagement vessel beforetransfer of liquid stream to the flash vessel, wherein the seconddisengagement vessel is at a lower pressure than the first disengagementvessel.
 33. The method according to claim 1 wherein at least a portionof diaryl carbonate is recovered from the dried liquid stream.
 34. Themethod according to claim 1 wherein at least a portion of diarylcarbonate is recovered from a liquid stream before water removal.
 35. Amethod for preparing diphenyl carbonate which comprises contactingphenol with oxygen and carbon monoxide in the presence of an amounteffective for carbonylation of a catalyst composition comprising thefollowing and any reaction products thereof: (A) at least one palladiumsource; (B) sodium bromide; (C) a metal co-catalyst selected from thegroup consisting of lead, cerium, copper, and titanium, and mixturesthereof; (D) at least one activating organic solvent; and (E)optionally, at least one base, wherein reaction water is removed by aprocess comprising the steps of: (vii) removing a liquid stream from anagitated oxidative carbonylation reaction mixture in a reaction vesseland transferring the stream to a first disengagement vessel which is notagitated; (viii) transferring a liquid stream from the firstdisengagement vessel to a flash vessel wherein the liquid stream issubjected to reduced pressure, whereby a majority of the water isremoved; (ix) returning at least a portion of a dried liquid stream tothe reaction vessel; and (x) optionally adding at least one of make-uparomatic hydroxy compound or other volatile constituent or catalystcomponent to the reaction vessel or to the dried liquid stream beforereturn to the reaction vessel, wherein at least a portion of diarylcarbonate is recovered from a liquid stream either before or after waterremoval.
 36. The method according to claim 35 wherein the reactionvessel and the first disengagement vessel are at essentially the samepressure and temperature.
 37. The method according to claim 35 whereinthe at least one palladium source is selected from the group consistingof palladium, palladium black, supported palladium, palladium/carbon,palladium/alumina, palladium/silica, inorganic palladium salts,palladium chloride, palladium bromide, palladium iodide, palladiumsulfate, palladium nitrate, organic palladium salts, palladium acetate,palladium oxalate, palladium (II) acetylacetonate, palladium complexes,PdCl₂(PhCN)₂, and PdCl₂(PPh₃)₂; the copper source is selected from thegroup consisting of copper alkoxides, copper aryloxides; copper salts ofP-diketones, and copper (II) acetylacetonate; the lead source isselected from the group consisting of lead oxides, PbO, Pb₃O₄, PbO₂;lead carboxylates, lead (II) acetate, lead (II) propionate; lead (II)nitrate, lead (II) sulfate; alkoxy lead compounds, lead (II) methoxide,aryloxy lead compounds, lead (II) phenoxide; lead (II) acetylacetonate,phthalocyanine lead, and tetraethyl lead; the titanium source isselected from the group consisting of titanium (IV) oxideacetylacetonate, titanium (IV) methoxide, titanium (IV) ethoxide,titanium (IV) butoxide, and titanium (IV) phenoxide; and the ceriumsource is selected from the group consisting of cerium acetate, ceriumsalts of β-diketones, and cerium (III) acetylacetonate, and theactivating organic solvent is tetraglyme.
 38. The method according toclaim 35 wherein the pressure is in a range of about 0.1-51 megapascalsand the temperature is in a range of about 50160° C. in the reactionvessel.
 39. The method according to claim 35 wherein the temperature ofthe liquid stream taken from the reaction vessel is maintained at aboutthe temperature of the reaction mixture from which the stream was takenbefore the liquid stream is subjected to reduced pressure.
 40. Themethod according to claim 39 wherein the temperature is about 50-160° C.41. The method according to claim 35 wherein a base is added
 42. Themethod according to claim 41 wherein the base is at least one of sodiumhydroxide or sodium phenoxide; or quaternary ammonium hydroxide orquaternary ammonium phenoxide.
 43. The method according to claim 41wherein the temperature of the liquid stream taken from the reactionvessel is lowered from the temperature of the reaction mixture fromwhich the stream was taken before the liquid stream is subjected toreduced pressure.
 44. The method according to claim 43 wherein thetemperature is about 50-100° C.
 45. The method according to claim 35wherein the pressure is in a range of about 0.7-53 kilopascals and thetemperature is in a range of about 50-160° C. in the flash vessel. 46.The method according to claim 45 wherein removal of water in the flashvessel is performed under essentially isothermal conditions.
 47. Themethod according to claim 45 wherein removal of water in the flashvessel is performed under essentially adiabatic conditions.
 48. Themethod according to claim 45 wherein removal of water in the flashvessel is performed under conditions between those of adiabatic andisothermal.
 49. The method according to claim 45 wherein removal ofwater in the flash vessel is performed at a temperature which is greaterthan 30° C. higher than the temperature in the reaction vessel.
 50. Themethod according to claim 45 wherein removal of water in the flashvessel is performed at a temperature which is greater than 30° C. lowerthan the temperature in the reaction vessel.
 51. The method according toclaim 35 which further comprises the step of transferring a liquidstream from the first disengagement vessel to a second disengagementvessel before transfer of liquid stream to the flash vessel, wherein thesecond disengagement vessel is at a pressure in a range of between about102 and about 345 kilopascals.
 52. The method according to claim 35wherein at least a portion of diaryl carbonate is recovered from thedried liquid stream.
 53. The method according to claim 35 wherein atleast a portion of diaryl carbonate is recovered from a liquid streambefore water removal.
 54. A method for preparing a diaryl carbonatewhich comprises contacting at least one aromatic hydroxy compound withoxygen and carbon monoxide in the presence of an amount effective forcarbonylation of a catalyst composition comprising the following and anyreaction products thereof: (A) at least one Group 8, 9, or 10 metalhaving an atomic number of at least 44 or a compound thereof; (B) atleast one alkali metal salt; (C) a metal co-catalyst comprising at leastone copper source and at least one titanium source; (D) at least oneactivating organic solvent; and (E) optionally, at least one base,wherein reaction water is removed by a process comprising the steps of:(i) removing a liquid stream from an oxidative carbonylation reactionmixture in a reaction vessel; (ii) transferring the liquid stream to aflash vessel wherein the liquid stream to subjected to reduced pressure,whereby a majority of the water is removed; (iii) returning at least aportion of a dried liquid stream to the reaction vessel; and (iv)optionally adding at least one of make-up aromatic hydroxy compound orother volatile constituent or catalyst component to the reaction vesselor to the dried liquid stream before return to the reaction vessel,wherein at least a portion of diaryl carbonate is recovered from aliquid stream either before or after water removal.
 55. The methodaccording to claim 54 wherein the aromatic hydroxy compound is phenol.56. The method according to claim 54 wherein the at least one Group 8,9, or 10 metal in component A is palladium.
 57. The method according toclaim 54 wherein the at least one palladium source is selected from thegroup consisting of palladium, palladium black, supported palladium,palladium/carbon, palladium/alumina, palladium/silica, inorganicpalladium salts, palladium chloride, palladium bromide, palladiumiodide, palladium sulfate, palladium nitrate, organic palladium salts,palladium acetate, palladium oxalate, palladium (II) acetylacetonate,palladium complexes, PdCl₂(PhCN)₂, and PdCl₂(PPh₃)₂.
 58. The methodaccording to claim 54 wherein the at least one alkali metal salt ofcomponent B is at least one salt selected from the group consisting ofhalides, chloride, bromide, tetrafluoroborate, and hexafluorophosphate.59. The method according to claim 58 wherein component B is at least onechloride or bromide salt.
 60. The method according to claim 59 whereincomponent B is an alkali metal bromide.
 61. The method according toclaim 59 wherein component B is an alkali metal chloride.
 62. The methodaccording to claim 54 wherein component C is a mixture of: at least onetitanium source selected from the group consisting of titaniumalkoxides, titanium aryloxides, titanium (IV) methoxide, titanium (IV)ethoxide, titanium (IV) isopropoxide, titanium (IV) 2-ethylhexoxide,titanium(IV) butoxide, titanium (IV) 2-ethyl- 1,3-hexanediolate,titanium(IV) phenoxide; titanium salts of β-diketones, titanium salts ofβ-ketoesters, titanium (IV) diisopropoxide bis(acetylacetonate),titanium (IV) bis(ethyl acetoacetato) diisopropoxide, and titanium (IV)oxide acetylacetonate); and at least one copper source selected from thegroup consisting of copper alkoxides, copper aryloxides; copper salts ofβ-diketones, and copper (II) acetylacetonate.
 63. The method accordingto claim 54 wherein the at least one activating organic solvent isselected from the group consisting of polyethers, nitriles, carboxylicacid amides, and sulfones.
 64. The method according to claim 63 whereinthe activating organic solvent is at least one member selected from thegroup consisting of diethylene glycol dialkyl ether, triethylene glycoldialkyl ether, tetraethylene glycol dialkyl ether, polyethylene glycoldialkyl ether, 15-crown-5, 18-crown-6; acetonitrile;N-methylpyrrolidinone, dimethylacetamide; and sulfolane.
 65. The methodaccording to claim 64 wherein the activating organic solvent istetraethylene glycol dimethyl ether.
 66. The method according to claim54 wherein component A is present in the amount of about 1 gram-atom ofmetal per 800-1,000,000 moles of aromatic hydroxy compound; component Bis present in the amount of about 1-2,000 moles per gram-atom of theGroup 8, 9, or 10 metal of component A; component C is present in theamount of about 0.1-200 gram-atoms of total metals per gram-atom of theGroup 8, 9, or 10 metal of component A; and component D is present in anamount of about 1-60% by volume based on the total volume of aromatichydroxy compound and component D.
 67. The method according to claim 54wherein at least one base, component E, is present in an amount in arange of about 0.1 to 5000 equivalents based on component A.
 68. Themethod according to claim 67 wherein the base is at least one alkalimetal hydroxide, onium hydroxide, alkali metal phenoxide, oniumphenoxide, guanidinium hydroxide or guanidinium phenoxide.
 69. Themethod according to claim 68 wherein the base is at least one alkalimetal hydroxide or alkali metal phenoxide.
 70. The method according toclaim 69 wherein the base is at least one of sodium hydroxide or sodiumphenoxide.
 71. The method according to claim 54 wherein the proportionof oxygen is about 1-50 mole percent based on total oxygen and carbonmonoxide.
 72. The method according to claim 54 wherein the pressure isin a range of about 0.1-51 megapascals and the temperature is in a rangeof about 50-160° C. in the reaction vessel.
 73. The method according toclaim 54 wherein the temperature of the liquid stream taken from thereaction vessel is maintained at about the temperature of the reactionmixture from which the stream was taken before the liquid stream issubjected to reduced pressure.
 74. The method according to claim 73wherein the temperature is about 50-160° C.
 75. The method according toclaim 54 wherein the temperature of the liquid stream taken from thereaction vessel is lowered from the temperature of the reaction mixturefrom which the stream was taken before the liquid stream is subjected toreduced pressure.
 76. The method according to claim 75 wherein thetemperature is about 50-90° C.
 77. The method according to claim 54wherein the pressure is in a range of about 0.7-53 kilopascals and thetemperature is in a range of about 50-160° C. in the flash vessel. 78.The method according to claim 77 wherein removal of water in the flashvessel is performed under essentially isothermal conditions.
 79. Themethod according to claim 77 wherein removal of water in the flashvessel is performed under essentially adiabatic conditions.
 80. Themethod according to claim 77 wherein removal of water in the flashvessel is performed under conditions between those of adiabatic andisothermal.
 81. The method according to claim 77 wherein removal ofwater in the flash vessel is performed at a temperature which is greaterthan 30° C. higher than the temperature in the reaction vessel.
 82. Themethod according to claim 77 wherein removal of water in the flashvessel is performed at a temperature which is greater than 30° C. lowerthan the temperature in the reaction vessel.
 83. The method according toclaim 54 which further comprises the step of transferring a liquidstream from the reaction vessel to a first disengagement vessel beforetransfer of liquid stream to the flash vessel, wherein the firstdisengagement vessel is not agitated.
 84. The method according to claim83 wherein the reaction vessel and the first disengagement vessel are atessentially the same pressure and temperature.
 85. The method accordingto claim 83 which further comprises the step of transferring a liquidstream from the first disengagement vessel to a second disengagementvessel before transfer of liquid stream to the flash vessel, wherein thesecond disengagement vessel is at lower pressure than the firstdisengagement vessel.
 86. The method according to claim 54 wherein atleast a portion of diaryl carbonate is recovered from the dried liquidstream.
 87. The method according to claim 54 wherein at least a portionof diaryl carbonate is recovered from a liquid stream before waterremoval.
 88. A method for preparing diphenyl carbonate which comprisescontacting phenol with oxygen and carbon monoxide in the presence of anamount effective for carbonylation of a catalyst composition comprisingthe following and any reaction products thereof: (A) at least onepalladium source; (B) sodium bromide; (C) a metal co-catalyst comprisingat least one copper source and at least one titanium source; (D) atleast one activating organic solvent; and (E) optionally, at least onebase, wherein reaction water is removed by a process comprising thesteps of: (vii) removing a liquid stream from an agitated oxidativecarbonylation reaction mixture in a reaction vessel and transferring thestream to a first disengagement vessel which is not agitated; (viii)transferring a liquid stream from the first disengagement vessel to aflash vessel wherein the liquid stream is subjected to reduced pressure,whereby a majority of the water is removed; (ix) returning at least aportion of a dried liquid stream to the reaction vessel; and (x)optionally adding at least one of make-up aromatic hydroxy compound orother volatile constituent or catalyst component to the reaction vesselor to the dried liquid stream before return to the reaction vessel,wherein at least a portion of diaryl carbonate is recovered from aliquid stream either before or after water removal.
 89. The methodaccording to claim 88 wherein the reaction vessel and the firstdisengagement vessel are at essentially the same pressure andtemperature.
 90. The method according to claim 88 wherein the at leastone palladium source is selected from the group consisting of palladium,palladium black, supported palladium, palladium/carbon,palladium/alumina, palladium/silica, inorganic palladium salts,palladium chloride, palladium bromide, palladium iodide, palladiumsulfate, palladium nitrate, organic palladium salts, palladium acetate,palladium oxalate, palladium (II) acetylacetonate, palladium complexes,PdCl₂(PhCN)₂, and PdCl₂(PPh₃)₂; the copper source is selected from thegroup consisting of copper alkoxides, copper aryloxides; copper salts ofP-diketones, and copper (II) acetylacetonate; the titanium source isselected from the group consisting of titanium (IV) oxideacetylacetonate, titanium (IV) methoxide, titanium (IV) ethoxide,titanium (IV) butoxide, titanium (IV) phenoxide; and the activatingorganic solvent is tetraglyme.
 91. The method according to claim 88wherein the pressure is in a range of about 0.1-51 megapascals and thetemperature is in a range of about 50-160° C. in the reaction vessel.92. The method according to claim 88 wherein the temperature of theliquid stream taken from the reaction vessel is maintained at about thetemperature of the reaction mixture from which the stream Was takenbefore the liquid stream is subjected to reduced pressure.
 93. Themethod according to claim 90 wherein the temperature is about 50-160° C.94. The method according to claim 88 wherein a base is added
 95. Themethod according to claim 94 wherein the base is at least one of sodiumhydroxide or sodium phenoxide; or quaternary ammonium hydroxide orquaternary ammonium phenoxide.
 96. The method according to claim 94wherein the temperature of the liquid stream taken from the reactionvessel is lowered from the temperature of the reaction mixture fromwhich the stream was taken before the liquid stream is subjected toreduced pressure.
 97. The method according to claim 96 wherein thetemperature is about 50-100° C.
 98. The method according to claim 88wherein the pressure is in a range of about 0.7-53 kilopascals and thetemperature is in a range of about 50-160° C. in the flash vessel. 99.The method according to claim 98 wherein removal of water in the flashvessel is performed under essentially isothermal conditions.
 100. Themethod according to claim 98 wherein removal of water in the flashvessel is performed under essentially adiabatic conditions.
 101. Themethod according to claim 98 wherein removal of water in the flashvessel is performed under conditions between those of adiabatic andisothermal.
 102. The method according to claim 98 wherein removal ofwater in the flash vessel is performed at a temperature which is greaterthan 30° C. higher than the temperature in the reaction vessel.
 103. Themethod according to claim 98 wherein removal of water in the flashvessel is performed at a temperature which is greater than 30° C. lowerthan the temperature in the reaction vessel.
 104. The method accordingto claim 88 which further comprises the step of transferring a liquidstream from the first disengagement vessel to a second disengagementvessel before transfer of liquid stream to the flash vessel, wherein thesecond disengagement vessel is at a pressure in a range of between about102 and about 345 kilopascals.
 105. The method according to claim 88wherein at least a portion of diaryl carbonate is recovered from thedried liquid stream.
 106. The method according to claim 88 wherein atleast a portion of diaryl carbonate is recovered from a liquid streambefore water removal.